One of the drawbacks inhibiting the introduction of a gasoline Homogeneous Charge Compression Ignited (HCCI) engine in production has been the lack of a simple, cost effective and energy efficient Variable Valvetrain Actuation (VVA) system to vary both the exhaust and intake events. Many electro-hydraulic and electro-mechanical “camless” VVA systems have been proposed for gasoline HCCI engines, but while these systems may consume less or equivalent actuation power at low engine speeds, they typically require significantly more power than a conventional fixed-lift and fixed-duration valvetrain system to actuate at mid and upper engine speeds. Moreover, the cost of these “camless” systems usually is on par with the cost of an entire conventional engine itself.
As the cost of petroleum continues to rise from increased global demands and limited supplies, the fuel economy benefits of internal combustion engines will become a central issue in their design, manufacture, and use at the consumer level. In high volume production applications, applying a continuously variable valvetrain system to just the intake side of a gasoline engine can yield fuel economy benefits up to 10% on Federal Test Procedure—USA (FTP) or New European Driving Cycle (NEDC) driving schedules, based on simulations and vehicle testing. HCCI type combustion processes have promised to make the gasoline engine nearly as fuel efficient as a conventional, 4-stroke Diesel engine, yielding gains as high as 15% over conventional (non-VVA) gasoline engines for these same driving schedules. The HCCI engine could become strategically important to the United States and other countries dependent on a gasoline based transportation economy.
Likewise, the use of a continuously variable valvetrain for both the intake and exhaust sides of a Diesel engine has been identified as a potential means to reduce the size and cost of future exhaust aftertreatment systems and a way to restore the lost fuel economy that these systems presently impose. By varying the duration of intake lift events, potential Miller-cycle type fuel economy gains are feasible. Also, with VVA on the intake side, the effective compression ratio can be varied to provide a high ratio during startup and a lower ratio for peak fuel efficiency at highway cruise conditions. Without intake side VVA, compression ratios must be compromised in a tradeoff between these two extremes. Exhaust side VVA can improve the torque response of a Diesel engine. Varying exhaust valve opening times can permit faster transitions with the turbocharger, reducing turbo lag. Exhaust VVA can also be used to expand the range of engine operation where pulse turbo-charging can be effective. Furthermore, varying exhaust valve opening times can be used to raise exhaust temperatures under light load conditions, significantly improving NOx adsorber efficiencies.
VVA devices for controlling the poppet valves in the cylinder head of an internal combustion engine are well known.
For a first example, U.S. Pat. No. 5,937,809 discloses a Single Shaft Crank Rocker (SSCR) mechanism wherein an engine valve is driven by an oscillatable rocker cam that is actuated by a linkage driven by a rotary eccentric, preferably a rotary cam. The linkage is pivoted on a control member that is in turn pivotable about the axis of the rotary cam and angularly adjustable to vary the orientation of the rocker cam and thereby vary the valve lift and timing. The oscillatable cam is pivoted on the rotational axis of the rotary cam.
For a second example, U.S. Pat. No. 6,311,659 discloses a Desmodromic Cam Driven Variable Valve Timing (DCDVVT) mechanism that includes a control shaft and a rocker arm. A second end of the rocker arm is connected to the control shaft. The rocker arm carries a roller for engaging a cam lobe of an engine camshaft. A link arm is pivotally coupled at a first end thereof to the first end of the rocker arm. An output cam is pivotally coupled to the second end of the link arm, and engages a corresponding cam follower of the engine. A spring biases the roller into contact with the cam lobe and biases the output cam toward a starting angular orientation.
A shortcoming of these prior art VVA systems is that both the SSCR device and the DCDVVT mechanism include two individual frame structures per each engine cylinder that are somewhat difficult to manufacture.
Another shortcoming is that these mechanisms “hang” from the engine camshaft and thus create a parasitic load. The SSCR input rocker is connected through a link to two output cams that also ride on the input camshaft. Because the mechanism comprises four moving parts per cylinder, it is difficult to design a return spring stiff enough for high-speed engine operation that can still fit in the available packaging space.
Still another shortcoming is that assembly and large-scale manufacture of the SSCR device would be difficult at best with its high number of parts and required critical interfaces.
What is needed in the art is a simplified VVA mechanism that is not mounted on the engine camshaft, is easy to manufacture and assemble, and requires minimal packaging space in an engine envelope.
It is a principal object of the present invention to provide variable opening timing, closing timing, and lift amplitude in a bank of engine intake or exhaust valves.
It is a further object of the invention to simplify the manufacture and assembly of a VVA system for such variable opening, closing, and lift.
It is a still further object of the invention to provide such a system which is not parasitic on the engine camshaft.